In a large skillet, heat the oil over medium heat. Add the onion, celery, and bell pepper and cook, stirring often, until the onion is softened, about 5 minutes. Add the rice and garlic and cook, stirring constantly, for 1 minute. Transfer the mixture to a 3 1/2 quart slow cooker.
Add the tomato juice, clam juice, water, Worcestershire sauce, thyme, oregano, salt, black and cayenne peppers, and break up the tomatoes with the side of a spoon. Cover and slow cook until the rice is barely tender, 5 to 6 hours on low.
Meanwhile, in a medium skillet over medium heat, cook the sausage, turning often, until browned, about 5 minutes.
During the last 15 minutes of cooking, stir the sausage, shrimp and scallops into the jambalaya. Increase the heat to high (300°) cover, and cook just until the shellfish are firm. Serve immediately.